JOHANNESBURG, South Africa -- An expert witness called by the defense team of South African Olympian Oscar Pistorius testified about bullet wounds, blood spatter, bruises, ballistics, sound, light, fibers and a toilet door -- but acknowledged Wednesday that he wasn’t a pathologist or ballistics expert and had no training in analyzing blood spatters.

Forensic geologist Roger Dixon initially was called in by the defense team to look at gunpowder residue. But under cross-examination he said he ended up looking at a wide range of issues in which he had little or no expertise.

Prosecutor Gerrie Nel accused him of irresponsibility for doing so.

“You gave evidence, you were strong about it,” said Nel, referring to pathology evidence Dixon offered. “Do you see how irresponsible it is to give evidence on areas you are not expert?”

Police ballistics expert Chris Mangena, pathologist Gert Saayman and another pathologist called by the defense, Jan Botha, all found that Pistorius’ girlfriend, Reeva Steenkamp, was hit by three bullets behind a door. Dixon determined she was hit four times.

Pistorius, the first athlete to compete in the Olympic Games on prosthetic limbs, shot and killed Steenkamp on Valentine's Day last year. Pistorius has pleaded not guilty to murder, contending he didn’t intend to kill anyone and didn’t consciously pull the trigger. He says he was in a state of terror, believing an intruder was about to come out the door.

Dixon was not present during the autopsy and based his findings on photographs.

He contested the state’s analysis that Steenkamp fell into a sitting position on a magazine rack after the first shot hit her in the hip.

Dixon testified that he had photographed white fibers on the Pistorius toilet door that matched up with Pistorius’ sock, backing the athlete’s story that he kicked the door with his prosthetic leg.

But under cross-examination by Nel, he admitted he only matched the fibers with the sock by looking at the photograph of the athlete wearing white socks. In fact he never held the socks.

“I did not examine the socks. I saw photographs of those socks being worn on the prosthesis at the scene,” he said. “I did not physically touch them.”

Nel planted more doubt over Dixon’s involvement in sound recordings of gunshots and a cricket bat hitting a door that were played in court. The defense contends that neighbors heard not shots but the sounds of Pistorious hitting the toilet door with a bat to break it down after the shooting.

Asked what expertise he applied in making the recordings, Dixon said he wielded the cricket bat while others played different roles. Dixon said he had no idea whether the person who recorded the sound had any expertise in recording gunshots and explosives.

As part of his preparation for the sound recording, “I went on the Internet to listen [to] sound bites that people use when they dub them into movies,” Dixon said.

He identified the sounds of shots on the recording played in court, but acknowledged he was not present when the gun was fired.

“To me it goes to the integrity of the witness,” Nel told the court. “Why would you identify gunshots if you weren’t there? It’s a serious issue to identify gunshots when he was not there.”

Although neither a wound ballistician nor a doctor, Dixon identified a bruise on Steenkamp’s buttock as evidence her back scraped against the magazine rack as she fell.

Pathologist Saayman, who has conducted about 15,000 autopsies, testified he opened up the wound and found it was caused by one of the hollow-point bullets fired by Pistorius, which broke up inside Steenkamp’s body after striking her hip.

South Africans were riveted by Nel’s tough cross-examination of Dixon, with the forensic expert’s name trending on Twitter. The most retweeted tweet in South Africa on Wednesday came from standup comedian, Lazola Gola: “Did Dixon find this gig on Gumtree?” -- a reference to a South African online classified advertising site.